1. Field of the Invention
The present invention relates to an SOI (silicon on insulator) substrate. The present invention also relates to a semiconductor device manufactured using the SOI substrate.
2. Description of the Related Art
In recent years, integrated circuits using an SOI substrate where a thin single-crystal semiconductor layer is formed on an insulating surface, instead of a bulk silicon wafer, have been developed. Since parasitic capacitance between a drain of a transistor and a substrate is reduced by using the SOI substrate, the SOI substrate has been attracted attention as a substrate which improves performance of semiconductor integrated circuits.
A Smart Cut (registered trademark) method is known as one of methods for manufacturing an SOI substrate (e.g., see Reference 1: Japanese Published Patent Application No. 2000-124092). An outline of a method for manufacturing an SOI substrate by a Smart Cut method is described below. First, hydrogen ions are implanted into a silicon wafer by an ion implantation method in order to form an ion implantation layer at a predetermined depth from the surface. And then, the silicon wafer into which the hydrogen ions are implanted is bonded to another silicon water with a silicon oxide film interposed therebetween. After that, by heat treatment, the ion implantation layer is to be a cleavage plane, and the silicon wafer into which the hydrogen ions are implanted is separated as a thin film, whereby a silicon film can be formed over the silicon wafer which is bonded to the silicon wafer into which the hydrogen ions are implanted. A Smart Cut method may also be referred to as a hydrogen ion implantation separation method.
On the other hand, as an example of techniques of forming a single-crystal silicon thin film over a glass substrate by such a Smart Cut method, a technique disclosed by the present applicant is known (e.g., see Reference 2: Japanese Published Patent Application No. H11-163363).